1. Field of the Invention
The present invention generally relates to a surface measurement apparatus and more specifically to a rolling digital surface measurement apparatus which measures and records the second elevation differences between a plurality of sequentially oriented, regularly spaced, co-linear points which lie on the surface being measured, and which then computes the elevations of the sequential points relative to a datum line established relative to any two points in the sequence by assuming that the mean curvatures of the tested surface are equal to zero in order to remove the inevitable effects of error compounding.
2. Description of the Prior Art
Various efforts have been made and a number of patents granted relating to the measurement of the profile or contour of a surface such as floor surfaces, roadway surfaces and the like. The following U.S. Pat. Nos. relate to this subject matter.
U.S. Pat. No. 2,335,390 PA1 U.S. Pat. No. 3,026,164 PA1 U.S. Pat. No. 3,056,209 PA1 U.S. Pat. No. 4,048,849 PA1 U.S. Pat. No. 4,084,324 PA1 U.S. Pat. No. 4,403,419 PA1 U.S. Pat. No. 4,434,558 PA1 U.S. Pat. No. 4,473,960
Prior U.S. Pat. No. 3,056,209 issued to Robert E. Oliver on Oct. 2, 1962 discloses a three wheel, continuous recording, analog computation device that endeavors to accurately measure the contours of a surface with respect to a reference plane by the use of a "floating" center wheel which produces a vertical displacement signal with respect to the distance travelled over the surface by a double integration procedure. Equations 1 through 4 in the Oliver patent describe the geometrical/mathematical relationships between the measured and desired quantities that make such a device theoretically possible. However, the patentee notes that it is necessary to consider stability problems and proceeds to change the ideal coefficients given in Equation 4 to certain values which the patentee found, through experience, to yield satisfactory results. The patentee justifies the abandonment of the ideal mathematical model as necessary to overcome serious problems of noise compounding that is inherent in all such integration devices (see column 5 of the Oliver patent). The patentee subsequently explains that the practical effect of changing the coefficients will be to damp out oscillations caused by noise signals and lists seven different pairs of alternative K2 and K3 values that were found useful. Apparently, the particular coefficient pair to be used will depend upon the wavelengths present in the surface being tested because changing the K2 and K3 coefficients effectively blinds the apparatus to certain signal frequencies as explained in column 5 of the Oliver patent and this fact is illustrated in FIG. 4 of the Oliver patent which shows regularly repeating "dead spots" in his computer response curve.
Accordingly, while Oliver and the other patents listed above relate to surface measurements, they do not disclose apparatuses equivalent to the present invention.